Cancer, in all its manifestations, remains a devastating disorder. Although cancer is commonly considered to be a single disease, it actually comprises a family of diseases wherein normal cell differentiation is modified so that it becomes abnormal and uncontrolled. As a result, these malignant cells rapidly proliferate. Eventually, the cells spread or metastasize from their origin and colonize other organs, eventually killing their host. Due to the wide variety of cancers presently observed, numerous strategies have been developed to destroy cancer within the body.
Typically, cancer is treated by chemotherapy, in which highly toxic chemicals are given to the patient, or by radiotherapy, in which toxic doses of radiation are directed at the patient. Unfortunately, these “cytotoxic” treatments also kill extraordinary numbers of healthy cells, causing the patient to experience acute debilitating symptoms including nausea, diarrhea, hypersensitivity to light, hair loss, etc. The side effects of these cytotoxic compounds limits the frequency and dosage at which they can be administered. Such disabling side effects can be mitigated to some degree by using compounds that selectively target cycling cells, i.e., interfering with DNA replication or other growth processes in cells that are actively reproducing. Since cancer cells are characterized by their extraordinary ability to proliferate, such protocols preferentially kill a larger proportion of cancer cells in comparison to healthy cells, but cytotoxicity and ancillary sickness remains a problem.
Another strategy for controlling cancer involves the use of signal transduction pathways in malignant cells to “turn off” their uncontrolled proliferation, or alternatively, instruct such cells to undergo apoptosis. Such methods of treating cancer are promising but a substantial amount of research is needed in order to make these methods viable alternatives.
The treatment and/or cure of cancer has been intensely investigated culminating in a wide range of therapies. Cancer has been typically treated with surgery, radiation and chemotherapy, alone or in conjunction with various therapies employing drugs, biologic agents, antibodies, and radioactive immunoconjugates, among others. The common goal of cancer treatment has been, and continues to be, the elimination or amelioration of cancerous tumors and cells with minimal unpleasant or life-threatening side effects, due to toxicity to normal tissues and cells. However, despite efforts, these goals remain largely unmet.
Tetracycline and a number of its chemical relatives have been used as antibiotics. The parent compound, tetracycline, has the following general structure:
The numbering system for the multiple ring nucleus is as follows:

Tetracycline, as well as the 5-OH (terramycin) and 7-Cl (aureomycin) derivatives, exist in nature, and are all well known antibiotics. Semisynthetic derivatives such as 7-dimethylamino-tetracycline (minocycline) and 6α-deoxy-5-hydroxy-tetracycline (doxycycline) are also known antibiotics.
However, changes to the basic structure of the ring system, or replacement of substituents at positions 1-4 or 10-12, generally lead to synthetic tetracyclines with substantially less, or essentially no, antibacterial activity. For example, 4-de(dimethylamino)tetracycline is commonly considered to be a non-antibacterial tetracycline.
Tetracycline compounds affect protein synthesis and appear to have anti-inflammatory properties in addition to their anti-microbial properties which are useful for treatment of arthritis. The anti-inflammatory activity of tetracycline compounds make them useful for treating other inflammatory disorders, even in the absence of an infectious agent. Tetracycline compounds can inhibit enzymes associated with inflammatory diseases such as matrix metalloproteases (MMPs), collagenase, gelatinase and elastase. While it is widely thought that tetracycline compounds decrease enzyme activity by chelation, they may also decrease inflammation by decreasing production of proinflammatory or other compounds. Tetracycline compounds may be effective when used with other compounds in the treatment of inflammatory conditions.
More recently, it has been established that tetracyclines, which are rapidly absorbed and have a prolonged plasma half-life, exert biological effects independent of their antimicrobial activity (Golub et al. 1991, Golub et al. 1992, Uitto et al. 1994). Such effects include inhibition of matrix metalloproteinases (abbreviated “MMPs”), including collagenases (MMP-1; MMP-8; MMP-13) and gelatinases (MMP-2; MMP-9), as well as prevention of pathologic tissue destruction (Golub et al. 1991).
In view of the above considerations, it is clear that there is a need to supplement existing methods of inhibiting cancer cell invasiveness and metastasis. Current approaches rely on highly cytotoxic compounds that cause ancillary debilitating sickness in patients, or use methodology that is expensive, procedurally difficult, and unpredictable.